Abstract
Uniparental disomy (UPD) is often considered as an event to be characterized exclusively by molecular genetic or epigenetic approaches. This review shows that at least one third of UPD cases emerge in connection with or due to a chromosomal rearrangement. Thus, additional (molecular) cytogenetic characterization of UPD cases is essential. Up to now > 1,100 UPD cases detected in clinical, non-tumor cases are reported in the literature. Recently, these cases were summarized in a regularly updated, freely available online database http://www.med.uni-jena.de/fish/sSMC/00START-UPD.htm. Based of this, here the presently known imprinting syndromes, the chromosomal contribution to UPD phenomenon, and the cytogenetic subgroups of UPD, including cases with normal, abnormal balanced or unbalanced karyotype (like e.g. small supernumerary marker chromosomes and Robertsonian translocations) and segmental UPD are reviewed. Furthermore, chromosome fragmentation as a possible mechanism of trisomic rescue is discussed, which might help to explain the observed 1:9 rate of maternal versus paternal UPD present in cases with original trisomic karyotypes. Overall, as UPD is more but an interesting rarity, the genetic background of each "UPD-patient" needs to be characterized besides by molecular methods, also by molecular cytogenetics in detail.
Highlights
Uniparental disomy (UPD) is the presence of a chromosome pair derived only from one parent present in a disomic cell line [1]
This review focuses on UPD present in clinically normal and clinically abnormal persons
As up to present only de novo small supernumerary marker chromosomes (sSMC) were associated with a UPD, trisomic rescue is the most likely reason for their formation
Summary
Uniparental disomy (UPD) is the presence of a chromosome pair derived only from one parent present in a disomic cell line [1]. As up to present only de novo sSMC were associated with a UPD, trisomic rescue is the most likely reason for their formation This assumption was already proven for some UPD cases Trisomic rescue can lead to sSMC formation and, more often, to mosaic formation like mos 47, XN, + 16/46, XN; in such cases a UPD, in the given example a UPD 16, can be present in the cells with normal karyotype. Together with the recent findings that there are inherent epigenetic differences between the paternal and maternal pronuclei in early cleavage stage embryos [40] This led us to suggest the following idea to explain the http://www.molecularcytogenetics.org/content/3/1/8 above mentioned 1:9 rate of matUPD versus patUPD. Evidence for the existence of a chromosome counting mechanisms in zygote and early embryogenesis was already provided [41]
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